This invention relates generally to apparatus and methods useful in scientific research and interventional medicine, and useful in the visualization and analysis of organic tissues and bodies; and to research into the cause and symptoms of disease, its diagnosis and treatment. The invention particularly concerns apparatus which may be advantageously utilized by a researcher, physician or health care professional, in conjunction with types of medical imaging equipment, such as computed tomography (CT) imaging equipment or magnetic resonance (MR) imaging equipment, plain film, radioscopy or fluoroscopy. The invention may be utilized to conveniently and accurately aid in timely (real time), manually, truly, and physically accomplishing the steps of locating, vectoring, and inserting an object such as a probe or other needle-like medical device at, toward, and in a patient""s targeted anatomic feature.
This invention relates to a stereotactic device for use with imaging apparatus, such as magnetic resonance imaging (xe2x80x9cMRIxe2x80x9d), CT, radioscopy or fluoroscopic apparatus, useful in the visualization and analysis of organic tissues and bodies, and to research into the cause and symptoms of disease, its diagnosis and treatment.
Many stereotactic devices for imaging are currently available. Despite the incredible power of many existing imaging technologies, surprisingly few procedures are actually done using these technologies in a routine clinical setting using any type of stereotactic assistance. There are several reasons for the lack of general acceptance of these devices in existing markets.
Most of these systems are expensive. Normally this expense cannot be justified in terms of usage or benefit for the large capital investment required. Physicians and hospitals are generally not prepared in today""s economic climate to make a large investment for a system that may only be used intermittently and may become quickly outdated.
Most existing systems are electronic and use optical and computer interfaces. The majority of these systems do not function in a real-time setting, but rather use special post-processed acquired image information. This information is then used to direct the procedure at a different time and place.
Many of the systems are vendor proprietary or dependent, so it is possible that only a few units may be able to use a specific technology. Though these systems claim to have very high real-space accuracy, in reality they have only limited real-space correlation since there is no live (real-time) imaging to confirm the progress of the procedure.
Most stereotactic units are complex and have multiple components. Some of the systems envelop the patient, such as through the use of head frames bolted directly to the skull. If there is any change in the components of such a rigid system at the time and place of the actual intervention, the previously obtained information that forms the basis for the intervention is no longer valid.
These systems also rely on gathering many images to direct the operation, rather than needing only a few. Because of this, the process can be very slow, since a large amount of data needs to be acquired to direct the process.
A number of existing stereotactic systems utilize fiducials that are placed on the patient or the stereotactic frame. These are image-conspicuous markers that are seen in the image space and in real-space. Utilizing this information, the virtual reality space depicted on the images is then fused with the real-space.
There are a number of devices that attach directly to the scanner, but these are generally cumbersome and have not been used extensively.
There are also a few systems that use very limited vector trajectories (of only a few angles). These are of little value since the limited number of approaches they provide to the target may not be enough to address the complicated anatomy, therapeutic devices, and goals of a variety of procedures.
Currently there are a number of rapid CT or MRI data acquisition systems available, but they have the disadvantages of being proprietary and of exposing the patient and operator to increased radiation dosage. These CT systems are analogous to fluoroscopy.
There are a few combined CT and fluoroscopic stereotactic systems. These have the potential to be very versatile, but they are complex proprietary systems. There are also a number of open magnet designs, but these are limited by vendor design. Critical information used to direct the procedure or intervention is based on artifacts from the needle or probe rather than on accurate real-time real-space information. The inherent imaging problems created by these artifacts limit the accuracy of these devices. In general the image quality of the fast imaging systems is not as good as routine imaging techniques.
FIG. 1 is a schematic of an enveloping frame that is used for head stereotactic systems of the prior art. The vertical lines 1 of the box represent the vertical struts, the horizontal lines 2 are crossing members used to define the section plane, the angled lines 3 represent cross-members, and the sphere 4 is the target. This frame is bolted or rigidly fixed to the patient and then imaged with many sections. The information gathered is used at a later time and place. Without real-time real-space confirmation during the intervention, there is no absolute confirmation that the previously determined plan is actually being correctly implemented.
FIG. 2 is a schematic of an image obtained from such a fixed frame rigid system. The vertical members 1 are seen at the corners of the square. The cross-members 3 are used to define the slice location and the target 4. There is no intuitive information that an operator can use to confirm that the information is accurate. Typically, a second system is used to actually execute the procedure at a later time with no real-time real-space confirmation of the previously obtained plan.
FIG. 3 shows an example of an MRI image 5 showing the use of a fixed frame stereotactic unit used for head imaging. The head 6 appears in the center of the image, with the target labeled in the left temporal bone. Also visible are the rods 7 (such as horizontal, vertical and cross-members 1, 2 and 3 shown in FIG. 2) surrounding the skull of the patient as a fixed device. The information is acquired by taking multiple images that must be post-processed.
There are a number of limitations to this type of device. The constituent support tubes are necessarily relatively large (in order to support the static arrangement), and thus cause a certain degree of inherent error in the system. The image shown is a single image that provides no real-time information that an operator might use during an image-monitored procedure. Also, a further error factor arises because the tubes are relatively distant from the target site, and the image itself is not without distortion, making the system distortion sensitive. Also, if the subject is moved then the system cannot be readily realigned.
A number of computer-based virtual reality systems"" disadvantages have been mentioned. The most important of these is that they provide no real-time confirmation at the actual time of intervention. All of these systems use specially acquired post-processed images that assume the virtual reality of the previously obtained imaging information and the true reality at the time of the actual intervention are identical. These systems are expensive, large, and can only be used in select locations.
There remain problems associated with fast, open, and combined technology systems. All are expensive, vendor specific and, as such, are limited to only a few sites. They are such complicated systems that any minor problem can render them useless, such as if the batteries on an LED were to stop working. They have limited real-space accuracy since they have problems with partial volume averaging and other imaging artifacts. Using these systems it may be difficult to track more than one device being used at a time.
Accordingly, the criteria for an improved stereotactic device include:
1. Accuracy in the form of mm level control and live image confirmation.
2. Ability to make rapid adjustments (preferably by remote control), and the use of a single image.
3. Flexibility in the form of multiple dimension adjustability, and the accommodation of a wide variety of probes.
4. Intuitive use through clear, non-computer-generated interpretation of electronic image information.
5. Simple construction; a device that may be compact enough to fix the imager on the patient and inexpensively constructed, and may be of disposable materials.
6. Applicability independent of site and imaging device.
Accordingly, there remains a need for relatively inexpensive stereotactic devices that may be used with a wide variety of imaging systems for the performance of varied procedures, and that may be used with any number of invasive devices and techniques.
The present invention defines stereotactic vectors requiring no electronic components. The present invention includes a stereotactic device for cross-sectional imaging.
The theory upon which the present invention is based is that two points define a line. The line is used as the vector that an appropriate medical device is advanced along to contact a target located inside the patient. With this device, a target may be contacted by a medical device (e.g. probe) using a minimum of two or three images.
The two points defining the vector outside of the patient""s body are determined using two sets of non-parallel image-conspicuous lines. The sets of non-parallel image-conspicuous lines may be derived from a number of standard geometric shapes.
The following paragraphs describe the geometric shapes preferred in development of an image-conspicuous pattern used by a stereotactic device of the present invention. It should be duly noted that other geometric shapes may provide similar results and that the examples given below are not intended to limit the invention.
FIG. 4 shows a triangle 40 that may provide the basis of design for a stereotactic device in accordance with one embodiment of the present invention. The triangle 40 shown is an isosceles triangle (i.e. two equal sides). However, any triangle may be adapted to perform the functions as described with the isosceles triangle. The triangle 40 has a first side 40a, a second side 40b and a third side 40c. The first side 40a is equal in length to the second side 40b. The first side 40a and the second side 40b are preferably made from an appropriate image-conspicuous material. The third side 40c may be used to align a stereotactic device on the patient by placing the third side parallel to the image plane.
Preferably, spanning the distance between the first side 40a and the second side 40b are span lines 42. The span lines 42 are parallel to the third side 40c. The span lines 42 are preferably equidistant from one another. The span lines 42 are preferably constructed of image-inconspicuous material. Along either the first side 40a or the second side 40b are span numbers 43 indicating the length of corresponding span lines 42. In a preferred triangle, the length of the span lines 42 corresponds to the distance of the span line to the angle defined by the first side 40a and the second side 40b. Alternatively, the distance between the first side 40a and the second side 40b is identified by appropriate markings along either the first side 40a, the second side 40b or both first side 40a and second side 40b. An appropriate marking is one that allows the user to positively identify and locate the distance between the first side 40a and the second side 40b. 
Preferably, a set of offset lines 44 spans the distance between the second side 40b and the third side 40c running parallel to the first side 40a. The offset lines 44 are preferably equidistant from one another and preferably constructed from an image-conspicuous material so as to appear on an image. Offset numbers 45 indicate the distance of corresponding offset lines 44 from the first side 40a.
A reference 41 constructed of image-conspicuous material aids the medical professional in interpreting an image taken by providing a mark on said image thereby eliminating confusion about right-left orientation of the pattern on the patient.
A distance between the first side 40a and the second side 40b parallel to the third side 40c shall be referred to as a chord 48. Each chord is a unique length because the first side 40a and the second side 40b are non-parallel. The entry point 47 is defined by a chord 48 and an offset 46. The offset 46 is the distance from the first side 40a to the entry point 47 along a chord 48. Alternatively, the chord 48 may be thought of as a slice location because it indicates the slice that the imaging machine operated upon.
FIG. 5 shows a quadrilateral 50 that may provide the basis of design for one embodiment of the present invention. Quadrilateral 50 has a first side 50a, a second side 50b, a third side 50c and a fourth side 50d. The second side 50b is parallel to the fourth side 50d. The third side 50c forms a right angle with both the second side 50b and the fourth side 50d. The third side 50c is not parallel to the first side 50a. Preferably, the first side 50a and the third side 50c are made from an appropriate image-conspicuous material. The fourth side 50d is used to align the stereotactic device on the patient parallel to the image plane.
Preferably, spanning the distance between the first side 50a and the third side 50c are span lines 52. The span lines 52 are parallel to the second side 50b and the fourth side 50d. The span lines 52 are preferably equidistant from one another. The span lines 52 are preferably constructed of an image-inconspicuous material. Along either the first sdie 50a or the third side 50c are span numbers 53 indicating the length of corresponding span lines 52. Alternatively, the distance between the first side 50a and the third side 50c is identified by appropriate markings along either the first side 50a, the third side 50c or both first side 50a and third side 50c. An appropriate marking is one that allows the user to positively identify and locate the distance between the first side 50a and the third side 50c. 
Preferably, offset lines 54 span the distance between the second side 50b and the fourth side 50d parallel to the first side 50a. The offset lines 54 are preferably equidistant from one another and constructed of an appropriate image-conspicuous material so as to appear on an image. Offset numbers 55 indicate the distance of corresponding offset lines 54 from the first side 50a. 
A reference 51 constructed of image-conspicuous material aids the medical professional in interpreting an image taken by providing a mark on said image thereby eliminating confusion about orientation of the pattern on the patient.
A distance between the first side 50a and the third side 50c parallel to the second side 50b and the fourth side 50d shall be referred to as a chord 58. Each chord is a unique length because the first side 50a and the third side 50c are non-parallel. The entry point 57 is defined by a chord 58 and an offset 56. The offset 56 is the distance from the first side 50a to the entry point 57 along a chord 58.
FIG. 6 shows a trapezoid 60 that may provide the basis of design for one embodiment of the present invention. Trapezoid 60 has a first side 60a, a second side 60b, a third side 60c and a fourth side 60d. The first side 60a and the third side 60c are parallel. The second side 60b and the fourth side 60d are not parallel to one another. Preferably, the second side 60b and the fourth side 60d are of equal length. The second side 60b and the fourth side 60d are preferably made of an appropriate image-conspicuous material. The first side 60a is used to align the stereotactic device on the patient parallel to the image plane.
Preferably, spanning the distance between the second side 60b and the fourth side 60d are span lines 62. The span lines 62 are parallel to the first side 60a and the third side 60c. The span lines are preferably equidistant from one another. The span lines 62 are preferably constructed of an image-inconspicuous material. Along either the second side 60b or the fourth side 60d are span numbers 63 indicating the length of corresponding span lines 62. Alternatively, the distance between the second side 60b and the fourth side 60d is identified by appropriate markings along either the second side 60b, the fourth side 60d or both second side 60b and fourth side 60d. An appropriate marking is one that allows the user to positively identify and locate the distance between the second side 60b and the fourth side 60d. 
Preferably, offset lines 64 span the distance between the first side 60a and the third side 60c parallel to the second side 60b. The offset lines 54 are preferably equidistant from one another and preferably constructed from an image-conspicuous material so as to appear on an image. Offset numbers 65 indicate the distance of corresponding offset lines 64 from the second side 60b. 
A reference 61 constructed of image-conspicuous material aids the medical professional in interpreting an image taken by providing a mark on said image thereby eliminating confusion about right-left orientation of the pattern on the patient.
A distance between the second side 60b and the fourth side 60d parallel to the first side 60a shall be referred to as a chord 68. Each chord is a unique length because the second side 60b and the fourth side 60d are non-parallel. The entry point 67 is defined by a chord 68 and an offset 66. The offset 66 is the distance from the second side 60b to the entry point 67 along a chord 68.
FIG. 7 shows the relationship of the lines of an image-conspicuous pattern 70 that includes a first image-conspicuous line 71 and a second image-conspicuous line 72. It has already been said that the two lines cannot be parallel to one another for the present invention to operate. In fact, a preferred angle 75 between the first image conspicuous line 71 and the second image-conspicuous line 72 is 53 degrees. If the image-conspicuous pattern 70 were derived from a triangle, then the first image-conspicuous line 71 would intersect the second image-conspicuous line 72. However, if the image-conspicuous pattern were derived from other geometric shapes, the image-conspicuous lines may need to be extended to accurately measure the angle 75. A first extension 73 is drawn from image-conspicuous line 71. A second extension line 74 is drawn from image-conspicuous line 72. The point where the first extension 73 intersects the second extension 74 is referred to as the intersection point 76. Having identified the intersection point 76, angle 75 may be measured.
At an angle of 53 degrees, the device pattern has a unique characteristic. The distance 78 between the first image conspicuous line 71 and the second image-conspicuous line 72 of the pattern measured on an image when the slice symmetrically crosses the pattern (parallel to the base of the triangle, not shown) is equal to the distance 77 between the intersection point 76 and the image plane (not shown). Note that independent of where the image slice crosses the pattern, the distance from the intersection of the two limbs is encoded on the image by the pattern being of an image-conspicuous material. This relationship allows for immediate exact definition of the location of the section plane in real-space on the pattern using only this simple image information.
The device of the present invention is in part based on a unique image pattern that encodes exact dimensional information (e.g., in mm) on each image that is directly related to the identical dimensional positions (e.g., in mm) in real-time and 3D space. This means there is no need for computers or any other type of complex translation of the image information to utilize data in the real-time space of the image system.
The pattern generated by devices of the present invention, in its preferred embodiment, is based on a specific geometric oddity. A triangle formed in a square has this property when the base of the triangle is the base of the square and the apex of the triangle is the midpoint of the top of the square. The triangle formed in this specific situation is a special isosceles triangle of about 53 degrees. The pattern of the preferred inventive device uses the limbs of this triangle. The limbs of the preferred device pattern are made of image-conspicuous materials. A similar geometric relationship between two image-conspicuous limbs can be obtained using a right triangle with a 45-degree apex, but this has a number of functional limitations, therefore the 53-degree design is preferred. When the imaging section plane is parallel to the pattern it produces a set of unique imaging and real-space characteristics. The true distance between the limbs of the device""s image-conspicuous pattern as measured on the image is equal to the true distance from the intersection apex of the pattern limbs. There is no need for a computer to tell the operator when this occurs or for complex calculations. The slice location is encoded as a true linear measurement on the image.
The distance from one reference limb of the device""s image-conspicuous pattern to a vector line measured on the image can be used to define the same point in real-space on the device.
For instance, when using CT, each limb of-the xe2x80x9cVxe2x80x9d may be made of an image-conspicuous material such as a metal wire. In the case of MRI, tubes (typically non-metallic; plastic) filled with contrast-enhanced fluid may be used as pattern limbs. The pattern may also be drawn directly on the patient, or included on an imager transparent material attached to the patient, such as through the use of adhesives. Examples may include a piece of flexible material, such as Mylar, provided with an adhesive on one side and bearing an image-conspicuous pattern (provided in the form of an attached image-conspicuous object in the shape of the xe2x80x9cVxe2x80x9d, or in the form of a printed design in the shape of the xe2x80x9cVxe2x80x9d in accordance with the present invention). Another example may be an adhesive strip, similar to an adhesive bandage, and provided with image conspicuous material members attached thereto, or an image-conspicuous xe2x80x9cVxe2x80x9d pattern printed thereupon.
Thus, one of the fundamental features of the preferred device is that it provides a three-dimensional alignment template that resides at a distance from the identified target point without having the target point located within the space defined by the three-dimensional alignment template. This allows the three-dimensional alignment template to be repositioned and to function accurately even if the tissue or patient has moved.
Preferably each of the above mentioned geometric shapes is adapted with an image-conspicuous means that can assist in identifying the offset of the entry point through that plane. Examples of preferred means include a set of parallel image-conspicuous lines adapted to appear as dots on an image that can be used to accurately measure the offset or as a moveable member adapted with image-conspicuous markers that appear as dots on an image to measure offset.
Generally, devices in accordance with present invention may be accurate to within 1 or 2 units (i.e., mm or less) of the limits of the image resolution. These levels of accuracy may be achieved independent of the section thickness and orientation.
Having fully described the geometric basis for the invention, we shall now discuss the general operation of the invention.
Initially, a skin point localizer is placed on the surface of the skin at a position where it is thought that entry into the body would be advantageous. The skin point localizer is constructed using a geometric shape (explained below). The geometric shape has at least two image-conspicuous lines capable of being captured by the imaging equipment. The skin point localizer is positioned such that the image plane is parallel to the offset line. An image is taken and the target is identified. The two image-conspicuous lines, having been properly oriented prior to imaging, show up on the image as two points. A vector may then be defined by drawing a line from the target through the space between the two points generated by the image-conspicuous material. Measurements are taken from the image such as the distance between the two image-conspicuous points and the distance from one of the points to the intersection of the line with the line that would be formed by connecting the two image conspicuous points. These measurements are the transferred to the skin point localizer. By measuring the distance between the two points the correct chord may be identified. The chord represents the slice location of the imaging device. By measuring the distance from one of the points to the intersection of the line with the line that would be formed by connecting the two image conspicuous points the offset may be identified. The skin point localizer defines a lower plane on the surface of the patient and the point through which an appropriate medical device will enter the patient. The skin point localizer is marked in an appropriate fashion and the patient is sterilzed, if necessary.
Alternatively, the skin point localizer may be a disposable item that is replaced, after marking the skin entry point and sterilizing the area, with a sterilized skin point localizer.
An upper plane apparatus, having at least two image-conspicuous lines, is then affixed onto the patient in such a manner as to capture the vector drawn onto the first image between its image-conspicuous lines. The upper plane apparatus is essentially parallel to the plane defined by the skin point localizer. It is important that the offset line of the lower plane device be parallel to the offset line of the upper plane apparatus. With the offset lines parallel to one another, the next image will enable the practitioner to accurately define and control the vector in three-dimensional space. A second image is then taken. From the second image, measurements similar to those taken from the first image are taken. Preferably, verifying the coordinates of the lower plane""s skin point localizer. The vector can be defined in terms of its intersection with the each plane (the first defined by the skin point localizer and the second by the upper plane apparatus) and the desired target. A suitable medical device may then be advanced along the vector so defined. The depth of insertion may additionally be measured from the image and used to ensure that the medical device is advanced the appropriate distance. Preferably, after the medical device has been inserted a short distance (typically a centimeter or two) a next image is taken to verify that the medical device is following the vector and that the alignment is correct so that contact with the target is achieved.
Examples of appropriate image-conspicuous materials include metal wire for computed tomography (CT) imaging equipment or barium paste or a liquid ink for magnetic resonance imaging (MRI) equipment.
In a real-time environment, the visual cues generated by the device-generated image-conspicuous pattern lead the operator to an exact real-time space location without the need of special computer information. The device and methods of the present invention may be used with any diagnostic or clinical imaging device, such as MRI, CT, or fluoroscopy devices. The device and methods of the present invention may also be used with industrial imaging devices in fields even outside of life sciences and medicine.
When an instrument is attached to a pattern device of the present invention, its position may be encoded independent of the slice thickness. Accordingly, partial volume artifact vector errors may be eliminated. The relationship of the instrument to the image may be encoded, a capability not possessed by known prior art devices.